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The ORF8 Gene Product of Agrobacterium rhizogenes TL-DNA Has Tryptophan 2-Monooxygenase Activity

July 2000 , Volume 13 , Number  7
Pages  787 - 790

Kai Lemcke , 1 Els Prinsen , 2 Harry van Onckelen , 2 and Thomas Schmülling 1

1Zentrum für Molekularbiologie der Pflanzen (ZMBP), Allgemeine Genetik, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany; 2University of Antwerp, Department of Biology, B-2610 Antwerp, Belgium

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Accepted 23 March 2000.

The open reading frame 8 (ORF8) is located on the TL-DNA of the phytopathogenic soil bacterium Agrobacterium rhizogenes strain A4. The predicted ORF8 protein has a particular structure and is possibly a natural fusion protein. The N-terminal domain shows homology to the A. rhizogenes rolB protein and may modulate the auxin responsiveness of host cells. The C terminus has up to 38% homology to tryptophan 2-monooxygenases (t2m). We show that ORF8 overexpressing plants contain a fivefold higher concentration of indole-3-acetamide (IAM) than untransformed plants. Protein extracts from seedlings and Escherichia coli overexpressing ORF8 show significantly higher turnover rates of tryptophan to IAM than negative controls. We conclude that the ORF8 gene product has tryptophan 2-monooxygenase activity.

Additional keywords: aux1 gene, auxin sensitivity, T-DNA.

© 2000 The American Phytopathological Society